1. Field of the Invention
The present invention relates to a one-way clutch for transmitting or cutting off driving force received from a driving source to a driven member in accordance with rotation direction, and relates to a driving transmission unit and an image forming apparatus using the one-way clutch.
2. Description of the Related Art
In various apparatuses, it is desired to rotate and drive multiple rotating members (driven members) using less number of motors (driving sources). For example, in an image forming apparatus, it is desired to rotate multiple developing sleeves using one motor, and rotate not only a developing sleeve but also a photosensitive member using one motor.
In a configuration for rotating multiple rotating members using one motor, it is desired to selectively rotate any given rotating member. For example, although not only the developing sleeve but also the photosensitive member are rotated using one motor, it may be desired to selectively rotate only the photosensitive member in some cases.
In reply to this request, a configuration has been made, in which a one-way unit (one-way clutch) is provided in a driving transmission path extending from a motor to rotating members, and the motor is rotated in the forward and backward directions to selective drive the rotating members (Japanese Patent Laid-Open No. 6-118784). In a generally-available one-way unit, multiple balls and needles are arranged in a peripheral direction, and therefore, there are many components, and the structure is complicated. Therefore, a small one-way clutch is expensive.
Japanese Utility Model Laid-Open No. 5-22867 suggests a one-way unit having a relatively small number of components and having a simple configuration. More specifically, this one-way unit includes an input gear and an output gear, and has a planet gear arranged in a space between an input gear and an inner gear of an output gear.
When a forward rotation driving force is received by the input gear, the planet gear is moved by the teeth of the inner gear provided on the output gear according to the rotation of the output gear with respect to the input gear. Accordingly, the teeth of the planet gear engages in a wedge-like manner with the gap formed by the edge portion provided on the input gear and the inner gear provided on the output gear. Therefore, the input gear and the output gear are integrally connected, and the driving which is received by the input gear is transmitted to the output gear.
When a backward rotation driving force is received by the input gear, the planet gear is moved in the direction opposite to that of the forward rotation by the teeth of the inner gear provided on the output gear according to the rotation of the output gear with respect to the input gear. Then, while the tooth tip of the planet gear slides on a cylindrical receiving portion provided on the input gear, it engages with the inner gear provided on the output gear, and because of the idle rotation, the driving force is not transmitted to the output gear.
However, the one-way unit described in Japanese Utility Model Laid-Open No. 5-22867 is arranged in the driving transmission path extending from the motor to the rotating member, and when the driving force in the direction in which the driving force is not transmitted to the output gear (backward rotation) is received by the input gear in order to selectively rotate the rotating member, nonperiodic hitting sounds of harmonics are generated. More specifically, the planet gear which idles on the cylindrical receiving portion provided on the input gear is in unstable condition in terms of the axial distance from the inner gear. In addition, the planet gear rotates at a higher speed than the input gear or the output gear. Therefore, this causes vibration with irregular hitting sounds, and abnormal sound is generated together with the tooth tip sliding sound.